Here is the full list of all 66 Torchlight achievements. It takes around 100-120 hours to unlock all of the achievements on Windows.
Catch 1000 fish
Catch 100 fish
Retire over 300 levels worth of characters
Kill 50,000 monsters
Drink 5,000 potions
Use 50 potions on your pet
Suffer 20 disenchants from the enchanter
Have an item disenchanted on the first enchantment attempt
Complete 50 Hatch Quests
Smash 1500 Breakables
Die 500 times
Kill 25 champion trolls
Sell 10,000 items to vendors
Achieved enlightenment by speaking with the horse 100 times
Catch 50 fish
Reach level 100
Successfully create 25 items using the transmuter
Achieve maximum fame
Achieve player level 100
Reach the 50th floor of a dungeon
Do at least 10,000 damage to an enemy in a single strike
Achieve player level 65
Complete 25 Gar Quests
Defeat Ordrak on Easy Hardcore
Defeat Ordrak on Normal Hardcore
Gamble 100 times
Retire two characters
Defeat Ordrak on Hard Hardcore
Complete 200 Quests
Gamble 50 times
Retire a character
Defeat Ordrak with no deaths
Defeat Ordrak on Hard
Defeat Ordrak on Very Hard
Defeat Ordrak on Very Hard Hardcore
Collect 250,000 gold
Take 25,000 steps
Beat the game with all three classes
Gamble 20 times
Gamble a unique item
Have 100,000 gold in your inventory
Permanently transform your pet
Successfully enchant one item 10 times
Successfully enchant one item 5 times
Kill 5000 Monsters
Transform your pet into a Mimic
Fill your pet's inventory
Defeat Ordrak on Easy or Normal
Defeat Ordrak in 8 hours or less
Defeat Ordrak in less than 5 hours
Defeat Alric
Defeat Medea
Change your pet by feeding it fish
Defeat Krag
Pull 100 levers
Defeat the Ember Colossus
Equip a spell on your pet
Defeat the Root Golem
Defeat the Overseer
Defeat Brink
Send your pet to town
Blow 25 enemies to pieces with critical strikes
1 game mod installed
5 mods installed at the same time
10 mods used at the same time
Find the entrance to the mine